Use proxy-agent instead of superagent-proxy

[szaboopeeter]

Use proxy-agent instead of superagent-proxy to get rid of vm2

Resolves: #5035, resolves: #5030, resolves: #4921

vm2 is a deprecated package with critical security issues.

For details see:

• https://www.npmjs.com/package/vm2
• GHSA-cchq-frgv-rjh5

@ionic-cli has vm2 in its dependency tree via superagent-proxy@3.0.0

There has been multiple issues and PRs in superagent-proxy about this. See TooTallNate/superagent-proxy#50 for example. But even after months, no solution has been taken in their repo. Which prompted many of the consumers of this library to just cut superagent-proxy and fall back to proxy-agent.

One such examples is Microsoft's appcenter-cli, whose approach I followed. Refer to for details on their corresponding PR: microsoft/appcenter-cli#2387

Note: proxy-agent has already gotten rid of vm2as a dependency: TooTallNate/proxy-agents#224

Test results

Tested the change locally by:

• Pointing Ionic CLI to local instance following the repo's Contribution Guide,
• setting HTTPS_PROXY env variable to a local proxy instance (Charles Proxy)

See below:

[szaboopeeter]

This solution is not complete, I'm not sure how I missed this - apparently the npm commands I ran to build/watch this were not building what I expected. Will close this for now, and re-open if I have time to clean it up.
But either way - reading through the discussions linked in the description I still think this is probably the best route to take sans superagent-proxy pushing a new version with upgarded proxy-agent.